Warmer months and shifting weather conditions will make some days hotter than others, and sometimes the heat may create dangerous conditions for prolonged exposure. Understanding the different types of heat and how heat affects our health could save a life. Let’s explore dry heat vs. humid heat, the warning signs for heat stress or heatstroke, and heat safety.
Dry Heat vs. Humid Heat
There are two main types of heat: dry heat and humid heat. Dry heat is present in most desert climates, while humid heat is present on the east side of the U.S., where moisture from the Gulf Coast flows northward.
Overall, the factors that play into what heat type is present in a given location is based on rainfall and humidity/moisture levels.
What Is Dry Heat?
- Dry heat occurs in any location with a combination of a temperature of 90 °F or above and relative humidity of 30% or less.
- Dry heat occurs most often in desert climates, like Phoenix and Las Vegas, that receive very little rain and moisture.
- Dry heat allows the body to cool more quickly, so you are less likely to get heat stress in an arid environment.
- Dry air allows more efficient evaporation than humid air, which is why you usually feel cooler in dry air — it has less moisture!
- Even in dry heat, prolonged exposure to direct sunlight in temperatures above 100 °F may cause heat-related medical issues.
What Is Humid Heat?
- Humid heat means the air is hot and moist, typically with a temperature at or above 90 °F and a relative humidity of 30% or more.
- Humid heat generally occurs east of the Rocky Mountains, where Gulf moisture flows northward during the warm season. Humid heat days occur infrequently in the Western U.S.
- Humid heat tends to be more dangerous as the moisture does not evaporate as efficiently, so more heat remains in the body.
Earth's How Zones
Just about every place in the U.S. gets hot weather. Alaska boasts a record high of 100 °F, Florida’s record maximum temperature is 109 °F, and California has seen 134 °F. There are three main factors that control where it gets hot and when.
Higher Sun Angle Equals More Heat
Places closer to the equator are often hotter than locations farther away because the sunlight is more direct at lower latitudes. Bismarck, North Dakota, is located at about 46 degrees north latitude, and Miami, Florida, at about 26 degrees north latitude. Which do you think has more hot days during the year? Miami easily wins the contest.
High-Pressure Pockets Move Heat Around
Large high-pressure zones develop during the summer months; the air sinks underneath the high and heats up. Summertime heat waves are often linked to these upper highs, and even northern cities like New York City or Chicago might make the news with scorching weather that lasts a week or two.
Mountains Make Desert
Look at a map of the world’s deserts — the Sahara, the Gobi, the Australian Outback, the American Southwest. All of them are surrounded by mountains that divert moist winds away and make for a big natural oven full of sand and rocks.
Heat Danger — Know the Signs
Sweat on the skin does not evaporate efficiently on humid days, so more of the heat remains trapped within your body. Thus, humid heat is more dangerous than dry heat. Heat sickness comes in the form of heat stress and heatstroke. Heatstroke can be fatal if immediate steps are not taken to cool the person off. In fact, heat-related issues kill more people in the U.S. every year than either lightning or tornadoes. Take decisive action if you observe warning signs of either heat stress or heatstroke.
Warning Signs of Heat Stress
Some of the signs of heat stress include:
- Nausea and vomiting
- Excessive perspiration
- Cool, clammy skin
A person experiencing heat stress should immediately move to a shaded location, preferably in an air-conditioned building, and be given plenty of fluids. Taking a cool shower or applying cold towels to the skin or forehead can also help relieve heat stress.
Warning Signs of Heatstroke
Heatstroke is more severe than heat stress and is a life-threatening medical emergency. Here are some telltale signs of heatstroke:
- Cessation of perspiration
- Red, hot, and dry skin
- Body temperature of 103 °F or greater
- Throbbing headaches and a rapid, strong pulse
Call 911 immediately if someone is experiencing heatstroke, and follow the heat stress procedures already outlined to cool them off. Act quickly — heatstroke is a killer.
Heat Safety Tips
A few simple precautions will help you avoid problems in the heat:
- Stay hydrated with water and electrolyte drinks
- Wear light-colored, loose-fitting clothing
- Take breaks from the sun or wear a wide-brimmed hat to reduce exposure
- Check the heat index, which factors in the air temperature and relative humidity, to help you determine how hot it actually feels (feels like temperature) to guide your day
Head into a cool building and drink plenty of fluids if you feel the symptoms of heat sickness.
Keep Ahead of the Heat
From yard work and gardening to kids running around at the park or even a casual outdoor party, closely monitoring humidity levels can help ensure everyone's safety and comfort. This is why AcuRite products, like a home weather station, incorporate both heat index and wind chill into the feels like temperature. The station will give you a quick and accurate assessment of outside temperature.
Regardless of what the temperature readings are, the feels like temperature is a good indication of the comfort index for your outdoor activities all year-round. Whether it's in dry or humid heat, may you always enjoy the great outdoors — and stay safe!
Steve LaNore is a certified broadcast meteorologist with more than 30 years’ forecasting and technical experience. He has provided meteorological consulting for everyone from insurance adjusters to courts and is a nine-time award-winning author and broadcaster. He has authored two books, available on Amazon. He resides in north Texas near beautiful Lake Texoma.